The present invention relates generally to the field of image forming, and more particularly to an image forming apparatus that varies the spacing between successive recording media based on the recording media supply level.
One of the carefully controlled functions in an image forming apparatus, such as a laser printer, is the control of the relative timing of image formation and the feeding of recording media. For laser printers using an intermediate transfer module in particular, coordination of the toner image formation on the photoconductors and/or intermediate transfer module and the feeding of paper to be printed so that both arrive at the appropriate transfer point at the same time is an important function. This task may be complicated somewhat, particularly in prior art multi-color printers, by the physical path lengths involved. In particular, it is common for the image path length between the farthest upstream toner cartridge and the relevant transfer point to be longer than the paper feed path length between the paper supply and the relevant transfer point. As such, it is common for toner image formation to start for a particular sheet before that sheet is xe2x80x9cpickedxe2x80x9d from the paper supply. That is, the image formation at that toner cartridge for sheet N begins substantially before the picking of the sheet N from the paper supply is initiated. Indeed, due to the geometries involved, the image formation for sheet N is typically initiated while the sheet Nxe2x88x921 is still being fed from the paper supply. As such, prior art devices often begin forming an image before it is possible to determine if the paper supply is empty. If this occurs, then toner is unnecessarily wasted.
The present invention provides a method and apparatus for conserving toner in an image forming apparatus, such as a laser printer, by varying the interpage gap when approaching an exhaustion of the recording media supply (e.g., a paper out condition). A supply level sensor is used to determine whether the supply of discrete recording media (e.g., paper sheets) is above or below a predetermined level, such as 5% or 10%. When the supply level is above the predetermined level the printer operates normally. That is, the interpage gap is at a first value, say two inches. With this arrangement, it is necessary for image formation for sheet N to begin prior to when a xe2x80x9cpaper out conditionxe2x80x9d would result from printing sheet Nxe2x88x921. When the sensed media supply level drops below the predetermined level, the interpage gap is automatically lengthened to a second value, such as approximately thirteen inches. This longer interpage gap allows for the exhaustion of the recording media supply that may result from printing of sheet Nxe2x88x921 to be determined prior to image formation beginning for sheet N. The interpage gap may be increased by allowing the ITM belt to continue moving, but without adding the image for sheet N+1 until after the xe2x80x9cpaper outxe2x80x9d would normally be sensed. For instance, the relative timing between the start of image formation and the picking of the corresponding sheet may be maintained (to maintain proper alignment at the relevant transfer point), but the start of image formation may be delayed until the xe2x80x9cpaper outxe2x80x9d would be detected if it exists after printing sheet Nxe2x88x921. If a xe2x80x9cpaper outxe2x80x9d condition is detected, the printer responds as usual (e.g., alerts user), but toner waste is reduced. This longer interpage gap/slower throughput process should be used when the media supply level is low, so that higher throughput is available for the majority of the time. The interpage gap may be reset to the normal value when it has been detected that the supply has been refilled to above the pre-determined level.